An outdoor wireless communication network typically includes a cell site having a base station, a cell tower, and a plurality of macro antennas mounted to the cell tower. The macro antennas are powered and arranged to transmit wireless broadband signals to communication devices, e.g., cell phones, within a defined area, typically, an area spanning about one (1) to two (2) miles. Received signals are transmitted upstream to a service provider and forwarded downstream to a destination cell tower or, if a cellular call spans a large distance such as might happen when making an international call, via a communications satellite.
The base station may include a tower, mounting a plurality of exterior antennas and Remote Radio Units (RRUs) and a ground shelter proximal to the tower, enclosing a variety of base station equipment. A plurality of exterior antennas and remote radio heads (RRHs) are mounted to the tower. Each RRH is operatively coupled, and mounted adjacent to, a group of associated macro antennas. Furthermore, each RRH manages the distribution of signals between its associated macro antennas and the base station equipment. The base station equipment may include electrical hardware operable to transmit/receive radio signals and to encrypt/decrypt communications with a mobile telephone switching office. The base station equipment also includes power supply units and equipment for powering and controlling the antennas and other devices mounted to the tower.
A distribution line, such as coaxial cable or fiber optic cable, distributes signals that are exchanged between the base station equipment and tower-mounted antennas however, transmission losses occur that can exceed several decibels. Remote radio heads are employed to mitigate such transmission losses. More specifically, RRHs move key base station radio frequency (RF) circuitry proximal to the macro antenna (“remotely” from the base station), to minimize the length of coaxial cable and the losses between the base station and the antenna. Additionally, remote radio heads typically have operation and management processing capabilities and a standardized optical interface to connect to the remainder of the base station.
Presently, each macro antenna may be configured to transmit up to nine hundred (900) distinct frequency bands or channels. While each antenna may transmit any one of the available frequency bands, RRUs are configured to uplink/downlink only a fraction of the total available bands due to a variety of technical and business issues, including the license fees associated with broadband usage, i.e., fees charged by the Federal Communications Commission or “the FCC.” Remote radio heads are routinely deployed and removed depending upon the availability of broadband signals and customer requirements. There is a burden associated with deploying RRHs which are configured for each of the many frequency bands transmitted by the service providers.
While the use of an RRH mitigates signal degradation, i.e., by minimizing the length of coaxial cable, the transition from fiber-to-cable (internally of the RRH) and from cable-to-fiber (internally of the antenna), continues to adversely impact signal performance and efficiency. Cabling internally of the tower-mounted antenna can also produce difficulties inasmuch as the internal space is confined and real estate at a premium.
Additionally, each of the existing towers is rated for a particular “sail load”, or load imposed by aerodynamic drag. As the number of radio heads increase on a cell tower, the aerodynamic drag increases as a function of the cumulative profile area. The additional drag may or may not be within the bending moment design criteria or allowables of the cell tower.
Finally, as number of broadband channels increase, i.e., the number which become available via the FCC, so too does the number of service providers. And, as the number of service providers increase, so too will the number of macro antennas and RRHs. As a consequence, the cost associated with managing the implementation of the new antennas and RRHs continues to grow. The present business environment requires a degree of flexibility which does not exist with the current RRHs/antenna systems employed in the field.
The foregoing background describes some, but not necessarily all, of the problems, disadvantages and shortcomings related to: (i) signal transmission losses between the base station and tower-mounted antennas, (ii) the need for multiple RRHs on a cell tower, (iii) the aerodynamic drag associated with multiple RRHs, and (iv) the deployment and complexity associated with multiple RRHs.